Why do we still have Colds and Flues, given that Sanitation and Nutrition Decreased many Major Diseases?

The mortality of major diseases such as smallpox, typhoid fever, plague, scarlet fever, diphtheria, whooping cough, cholera, dysentery declined due to improvements in nutritional, sanitary, social and economic conditions.

Mortality associated with influenza (flu) also declined in the 20th century. (Two references are below.)

To understand what these "diseases" are, we need to identify the difference between healing and disease. The pains and activities that are a dis-ease or ill-at-ease-ness to the patient are symptoms of disease to the diagnosing doctor and to the health scientist is evidence of the body's effort to heal. Several activities of the body are healing activities, primarily of a detoxifying nature. That is: Fever, rash, mucous and increased elimination are all activities of the body that are throwing out unnecessary materials that have either been introduced or buildup over time. Thus a balance is restored to the body when necessary.

In a society that has both poor sanitation and poor nutrition there will be lots of filth get into the body due to dirty water, stench in the air, partially decayed food, etc. Malnutrition will mean that the body can not safely and successfully detox the body and thus the disease will be both severe and accompanied by high mortality rates.

As nutrition becomes more widely available on a year around basis, the bodies power to self heal becomes more successful. That is, the prevailing diseases become safer and less severe.

As sanitation becomes more wide spread in society the incidence of infectious diseases also declines because bodies have less need for detoxing episodes.

So why today, with our improved sanitation and nutrition, do we still require frequent detoxing in the form of colds and flues.

Imbalance of our cellular chemistry occurs not only in response to external filth getting into the body but is also due to a build up of toxic materials in the body due to improper digestion and incomplete elimination of toxic materials on a day to day basis.

Modern eating habits often include overeating, eating when emotionally tense, incomplete chewing and eating foods containing "preservatives" which are poisons, etc. These factors cause a certain amount of toxic byproducts to be generated as a result of incomplete digestion.

Our highly processed foods, low fiber and lack of exercise cause incomplete elimination of the toxic byproducts and thus a buildup of toxic materials over time.

When the body has more toxic materials than it is proper to deal with such as often occurs after our holidays, then the body goes into a "emergency" form of detox which we call a cold because we have mucous being eliminated from various eye, ear, nose and throat membranes.

The flu is simply a more severe form of the same toxin eliminating mode of the body.

References:
Flu and Pneumonia http://vaclib.org/basic/fluindex.htm#graphs
Mortality from influenza and pneumonia combined did decline from about 200 deaths per 100,000 in 1900 to the 10-20 range per 100,000 recently.

http://www.ajph.org/cgi/content/abstract/AJPH.2007.119933v1American Journal of Public Health, 10.2105/AJPH.2007.119933
Results. An overall and substantial decline in influenza-classed mortality was observed during the 20th century, from an average seasonal rate of 10.2 deaths per 100 000 population in the 1940s to 0.56 per 100 000 by the 1990s.